Hereditary cataract (HC) in the Staffordshire bull terrier and the Boston terrier (known as juvenile HC in this breed) is an inherited condition. Clinical symptoms appear in the first year of life; cataracts always appear in both eyes and always progress to result in total blindness by the time the dog is about three years of age (see Barnett K C (1978) Hereditary cataract in the dog. J Small Anim Pract. February; 19(2):109-20).
The disease is inherited as a simple autosomal recessive condition meaning it is caused by a genetic mutation in a single gene and a dog has to inherit two copies of the mutation, one from each parent, for it to develop clinical symptoms. Dogs that inherit a single copy of the genetic mutation (carriers) are clinically clear of the disease.
Breeders wishing to avoid breeding affected dogs are hampered by the difficulty in identifying carriers, since such animals do not show any clinical signs of the disease but will pass the mutation to approximately half of their offspring.
U.S. Pat. No. 5,804,388 (“Chromosome 9 and progressive rod-cone degeneration disease genetic markers and assays”) discusses diagnostic methods for detecting the presence in a canine subject of at least one genetic marker that is genetically linked and co-segregating with a progressive rod-cone degeneration disease trait. However this disclosure is based on linkage only, and not to definitive association with a mutation causing a disease trait.
Thus it can be seen that the identification, characterisation, and genotyping of one or more markers associated with (for example) HC in the Staffordshire bull terrier (SBT) and the Boston terrier (BT), and methods using the same would provide a contribution to the art.